1. Field of the Invention
The present invention relates to a pneumatic tire for heavy loads for a construction vehicle or the like having both a low heat generation characteristic and a high wear resistance without sacrificing the working efficiency in manufacturing process of the tires. The invention further relates to a tire for construction vehicle for heavy loads, in particular, a pneumatic tire for heavy loads running on an unpaved road, excellent in heat generation characteristic, change of tire appearance, and wear resistance after traveling, and suppressed in a reduction of physical properties.
2. Description of the Related Art
Hitherto, in a pneumatic tire for heavy loads for rough roads, as a means for preventing heat generation, change of external appearance of the tire and reduction of wear resistance, and various physical properties, the carbon black to be blended in the tire tread rubber has been selected and the filling amount thereof optimized. Recently, various types of tread rubbers for pneumatic tires for heavy load containing silica, together with carbon black blended in the tread rubber composition have been proposed.
For example, JP-A No. 1-311141, JP-A No. 3-65406, and JP-A No. 4-226140 propose attempts to improve the wear resistance, cut resistance, heat generation characteristic and others by blending silica together with carbon black in the rubber composition for the tread of a pneumatic tire for heavy load for construction vehicles or the like.
Similarly, JP-A No. 3-84049 and JP-A No. 5-98074 propose attempts to improve the wear resistance, break resistance, low heat generation, tire appearance after traveling on a rough road and others by blending silica together with carbon black having a specific characteristic in the rubber composition for the tread of a pneumatic tire for heavy load.
Further, JP-A No. 61-287945 and JP-A No. 1-118551 disclose that heat generation and cut resistance can be improved by blending carbon black and silica in a rubber composition. Furthermore, JP-A No. 46-1688 discloses blending of carbon black and silica for preventing deterioration of mechanical properties of rubber products used in severe conditions such as tires.
However, in the pneumatic tire for heavy loads running on a rough road, a large distortion amplitude is applied repeatedly to the rubber composition disposed in the tread during travel, and the tire temperature is significantly raised, resulting in an extreme reduction of the life of the tire. On the other hand, conventionally, in order to improve the wear resistance of a pneumatic tire for heavy loads, it was attempted to change the types and amounts of fillers, but this resulted in a deterioration of the heat generation characteristic and working efficiency in tire manufacturing process, so that satisfactory results could not be obtained.
Further, these prior art references in which silica was compounded with carbon black in the rubber composition for the tread of the pneumatic tire for heavy loads, were not intended to improve both the heat generation characteristic after traveling, external appearance and wear resistance and to suppress reduction of physical properties of the tire, especially reduction of the breaking elongation (Eb) at a high temperature. That is, in the prior art, nothing was considered about suppressing of reduction of physical properties after drastic changes of the tread caused by running on a rough road, in addition to improvement of appearance characteristic, wear resistance and heat generation characteristic.